We are investigating the molecular mechanisms of the chemical reactions involved in the biological damage caused by trace levels of ozone and NO2 in air to lipids and to models of biological membranes. We also are studying the radicals present in cigarette smoke. Since most of the reactions we are studying involve free radicals, our project can be described as aimed at the elucidation of the mechanisms of the pathology caused by radicals. We have found that both ozone and NO2 initiate the autoxidation of unsaturated and polyunsaturated fatty acid esters. In addition, NO2 gives nitro-containing products. In the ozone and NO2 projects we are investigating the kinetics of the disappearance of fatty acids and the appearance of all of the products we can follow. In addition, we have begun a detailed separation and chemical identification for as many of the products as we can obtain in sufficient quantities. We have begun an effort at elucidating the nature of the radicals present in cigarette smoke using electron spin resonance.